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Installing the indoor unit
John Breeds explains how to get the best results
Paying detailed attention to Wiring and setting up the indoor unit to operate with the VCR and TV is all too often something that dish installers avoid--perhaps because they know, through experience, that if the TV or VCR unit goes faulty within a week or two of their visit they usually get the blame!
Inferior pictures, with odd patterning, is often a symptom of not exploiting each unit's features to get the best result.
Before making any connection whatsoever you should familiarise yourself with the equipment. Virtually all modern satellite receivers are supplied pre-tuned to popular programmes on satellites such as Astra, Eutelsat and Intelsat.
The satellite receiver decodes/de scrambles the satellite signals into a form which is easily handled by the TV. There are two common means of inputting a signal to a TV set.
One is the normal UHF aerial socket, and the other is a form of direct video connection. Sometimes you can feed the picture tube direct with RGB (red, green, blue) signals. The RGB and direct video (and audio) is usually fed via a Scart connection.
Most satellite receivers, which decode Pal signal, give two forms of output, i.e. a UHF signal which is tunable between say, UHF channels 3 - 39, and a direct video signal.
Other satellite receivers which process Mac signals sometimes output all forms of signal, i.e. RGB, Direct Video and UHF. In this instance you'll get better pictures by using the RGB signal, provided that the TV is equipped with a fully wired Scart connector.
The first thing to do is tune the TV into the UHF output channel of the satellite receiver. A switchable 'test bar' signal is often available, similar to the method used when tuning in VCRs. If there is no "TSG" or "Test" switch on the satellite receiver, press the "menu" button instead. If the customer requires the satellite receiver to be used with the VCR then wire the system as shown in Fig.2.
Tuning in the VCR
As an example, the UHF channel of the existing VCR's modulator could be Ch. 36. First, switch on the VCR's test bar. Tune the TV receiver to Ch. 36 to monitor and check how well the TV is tuned in and, if necessary, adjust the TV tuning. Now switch off the VCR's test bar.
Now comes the dodgy bit where you have to decide which TV program number to store the VCR's UHF modulator channel. Many older TV sets, with no Scart or Din inputs, allocate program number 0 or 10 for the VCR.
The reason for this is that the TV's AFC pull-in time constant is automatically increased on these program numbers and can therefore more easily cope with the unsteady fine synch signal from the video tape during the playback mode.
The tell-tale sign of AFC pull-in problems is the 'tearing-to-the-left' effect at the top of the screen during playback. Again this is more noticeable on older VCRs with poor line synch regulation during record and playback.
On most modern TV sets program number 0 to 10 switch the input circuitry to direct video modes, i.e., it will accept signals only via its Scart or Din socket. If this is so, and you have a choice, then store the VCR's UHF modulator channel on the TV's program number 5.
Tuning in the satellite receiver
Now connect the satellite receiver using the UHF loop-through facility. Adjust the TV to channel 33. Switch on the satellite receiver's test bar (or menu) and adjust its UHF modulator trimmer so that the bar (or menu) appears on screen. (Some receivers are tuned via the remote control). Fine tune the TV so that the test bar is sharp. Switch off the test bar. The satellite receiver's UHF modulator channel is usually saved and allocated on program number 6 of the TV set.
Tuning in the combined units
At this stage be especially aware of the intermodulation problems which are caused by two active UHF channels spaced apart by plus or minus 1, 5 or 9 channels. For example, intermodulation patterning on the TV screen results if the incoming TV channel is 41, and the VCR UHF output channel is 32, i.e. nine channels apart. The answer would be to adjust the VCR's modulator preset to eliminate the patterning.
The problem of intermodulation, and its solution, is slightly more complicated when a satellite receiver is introduced into the system. The UHF modulator employed in most VCRs and satellite receivers has a limited tuning range, i.e. Channels 30-39. Working with these limitations when receiving terrestrial signals in the Group A (Channels 21-34) and Group B (Channels 39-53) presents a bit of a challenge! This is an even greater problem now that TV channel 5 is broadcasting!
In practice, without the aid of a spectrum analyser and frequency counter, the only way to tune in is to connect the system as shown in Fig.2. Then adjust the modulator preset in the VCR and the satellite receiver to eliminate patterning on each test bar and all terrestrial channels. Fig.3.
Direct video Input/output Scart
For several years, many discerning viewers have enjoyed the improved picture (and sound) quality which results when their TV receiver is directly connected to the VCR by an audio and video lead.
Until recently, manufacturers had differing views on which types of sockets were best suited to the application. This led to a variety of products having an assortment of sockets, eg. BNC, Phono, Din, 'D' and 'J' Connectors and, of course, the Peritel which is more commonly call the Scart or Euroconnector.
Most manufacturers have now adopted the Scart and nearly all modern TVs, VCRs and satellite receivers come provided with Scart sockets.
The connector comprises 20 spade-shaped contacts in an insulated block, surrounded by an almost rectangular metal skirt which protrudes from a tapered plastic housing. The housing itself is of a wrap around construction held in place by a threaded collar used a cable clamp.
Most modern satellite receivers have two or three Scart sockets. The input/output routing of the VCR, satellite decoder and TV signals is programmed into the satellite receiver and TV memory during installation.
The Scart connector is described as a 21 pin non-reversible device. The metal skirt acts as the 21st connection which is connected to chassis.
There are up to 20 pins (plus screen) present on full specification connectors. But unused pins are usually removed when the connector is used for audio or audio-visual use. Usually the connections are crimped rather than soldered as this avoids the possibility of any shorts between the closely fitted pins.
The Scart connector output from the satellite receiver has direct video/sound signals available on its pins. The signal is then fed directly to the TV's Scart input, by-passing the RF and IF circuitry in the TV, resulting in slightly 'cleaner' pictures.
Pin 8 is the 'status' control or "here I am" signal. When the satellite receiver is switched on its TV Scart pin 8 goes 'high' to approximately 12 Volts. When the TV's Scart pin 8 is taken high (AV mode) its internal switching blocks off the signal from the UHF input and IF circuitry, and the TV then automatically receives satellite pictures via the direct video route.
Some TV receivers 'lock' to the AV mode when Scart pin 8 is held high, thus preventing the user from changing channels on the TV until the satellite receiver is switched from Sat to TV, or to its standby mode. One way to overcome this problem is to cut the Scart lead connection to pin 8. With pin 8 lead cut the satellite receiver will not be able to switch the TV to the AV mode automatically, hence the user will have to switch the TV manually to its own AV channel.
Nowadays, the number of available signal sources to the TV set such as VCRs, camcorders, home computers, satellite receivers, and particularly satellite decoders, has led to an interconnection nightmare for installers. The main problem is that most TVs and VCRs do not have the required number of Scart sockets, or scope of switching control, to manage the present and growing number of signal sources. the best arrangement is to avoid RF connections where Possible. making use instead of the video outputs available from VCRs and satellite TV receivers.
The multi-source of signals also poses other dilemmas. In addition to the direct video/sound connectors installers also need to consider the quantity of mains multi-sockets, mains to 9v adaptors, the connections and leads for the hi-fi unit for satellite radio, the arrangement of the RC handsets, and the space to fit all these boxes and cables!
Perhaps all modern houses should incorporate their own signal/switching control rooms as an added selling featured "
JohnBreeds has written several books about Satellite TV but is now doing childrens' parties.